A large number of relatively inexpensive still cameras are currently manufactured which provide an automatic focusing capability and/or automatic exposure control governed by either ambient illumination for outdoor photography or by a sensing of the object distance when used in flash mode. Ranging sensings used to govern lens focusing, as well as exposure during flash mode, are provided by a variety of systems. Ranging by ultrasonic pulses produced by the camera, electronic comparison of the images in a split-image rangefinder, and the reflected amplitude of an infra-red preflash all are well-described in the patent literature. In flash mode, exposure control is governed typically by one of the aforementioned range sensings, whereas in the ambient illumination mode, some form of weighted value of the scene illumination as detected by a photosensor is typically used to govern exposure.
In the case of intermediate and higher-priced cameras, such systems are routinely provided. On the other hand, in the case of the low-cost camera, the expense of providing such range-sensing systems becomes prohibitive. Moreover, such low-cost cameras are not in general purchased by for the serious amateur, but rather by people who either use a camera only on rare occasions, or who are relatively inexperienced, or both. Even the most rudimentary manual exposure and focus adjustments are frequently overlooked by such users.
Thus, there remains a need in the low-priced camera field for a completely automatic focus and exposure system which will give adequate results both as to focus and exposure in totally inexperienced hands.